The present invention relates to Clostridial toxin pharmaceutical compositions. In particular, the present invention relates to botulinum toxin pharmaceutical compositions and uses thereof.
A pharmaceutical composition is a formulation which contains at least one active ingredient (such as a Clostridial toxin) as well as, for example, one or more excipients, buffers, carriers, stabilizers, preservatives and/or bulking agents, and is suitable for administration to a patient to achieve a desired diagnostic result or therapeutic effect. The pharmaceutical compositions disclosed herein have diagnostic, therapeutic and/or research utility in patients such as humans, as well in, for example, canine, equine, bovine and porcine mammalian species patients, and in non-mammalian avian species patients.
For storage stability and convenience of handling, a pharmaceutical composition can be formulated as a lyophilized (i.e. freeze dried) or vacuum dried powder which can be reconstituted with a suitable fluid, such as saline or water, prior to administration to a patient. Alternately, the pharmaceutical composition can be formulated as an aqueous solution or suspension. A pharmaceutical composition can contain a proteinaceous active ingredient. Unfortunately, a protein active ingredient can be very difficult to stabilize (i.e. maintained in a state where loss of biological activity is minimized), resulting therefore in a loss of protein and/or loss of protein activity during the formulation, reconstitution (if required) and during the period of storage prior to use of a protein containing pharmaceutical composition.
Stability problems can occur because of protein denaturation, degradation, dimerization, and/or polymerization. Various excipients, such as albumin and gelatin have been used with differing degrees of success to try and stabilize a protein active ingredient present in a pharmaceutical composition. Additionally, cryoprotectants such as alcohols have been used to reduce protein denaturation under the freezing conditions of lyophilization.
Albumin
Albumins are small, abundant plasma proteins. Human serum albumin has a molecular weight of about 69 kiloDaltons (kD) and has been used as a non-active ingredient in a pharmaceutical composition where it can serve as a bulk carrier and stabilizer of certain protein active ingredients present in a pharmaceutical composition.
The stabilization function of albumin in a pharmaceutical composition can be present both during the multi-step formulation of the pharmaceutical composition and upon the later reconstitution of the formulated pharmaceutical composition. Thus, stability can be imparted by albumin to a proteinaceous active ingredient in a pharmaceutical composition by, for example, (1) reducing adhesion (commonly referred to as “stickiness”) of the protein active ingredient to surfaces, such as the surfaces of laboratory glassware, vessels, to the vial in which the pharmaceutical composition is reconstituted and to the inside surface of a syringe used to inject the pharmaceutical composition. Adhesion of a protein active ingredient to surfaces can lead to loss of active ingredient and to denaturation of the remaining retained protein active ingredient, both of which reduce the total activity of the active ingredient present in the pharmaceutical composition, and; (2) reducing denaturation of the active ingredient which can occur upon preparation of a low dilution solution of the active ingredient.
As well as being able to stabilize a protein active ingredient in a pharmaceutical composition, human serum albumin also has the advantage of generally negligible immunogenicity when injected into a human patient. A compound with an appreciable immunogenicity can cause the production of antibodies against it which can lead to an anaphylactic reaction and/or to the development of drug resistance, with the disease or disorder to be treated thereby becoming potentially refractory to the pharmaceutical composition which has an immunogenic component.
Unfortunately, despite its known stabilizing effect, significant drawbacks exist to the use of human serum albumin in a pharmaceutical composition. For example human serum albumins are expensive and increasingly difficult to obtain. Furthermore, blood products such as albumin, when administered to a patient can subject the patient to a potential risk of receiving blood borne pathogens or infectious agents. Thus, it is known that the possibility exists that the presence of albumin in a pharmaceutical composition can result in inadvertent incorporation of infectious elements into the pharmaceutical composition. For example, it has been reported that use of human serum albumin may transmit prions into a pharmaceutical composition. A prion is a proteinaceous infectious particle which is hypothesized to arise as an abnormal conformational isoform from the same nucleic acid sequence which makes the normal protein. It has been further hypothesized that infectivity resides in a “recruitment reaction” of the normal isoform protein to the prion protein isoform at a post translational level. Apparently the normal endogenous cellular protein is induced to misfold into a pathogenic prion conformation. Significantly, several lots of human serum albumin have been withdrawn from distribution upon a determination that a blood donor to a pool from which the albumin was prepared was diagnosed with Creutzfeldt-Jacob disease.
Creutzfeldt-Jacob disease (sometimes characterized as Alzheimer's disease on fast forward) is a rare neurodegenerative disorder of human transmissible spongiform encephalopathy where the transmissible agent is apparently an abnormal isoform of a prion protein. An individual with Creutzfeldt-Jacob disease can deteriorate from apparent perfect health to akinetic mutism within six months. Possible iatrogenic transmission of Creutzfeldt-Jacob disease by human serum albumin transfusion has been reported and it has been speculated that sufficient protection against Creutzfeldt-Jacob disease transmission is not provided by the usual methods of human serum albumin preparation which methods include disposal of blood cellular elements and heating to 60 degrees C. for 10 hours. Thus, a potential risk may exist of acquiring a prion mediated disease, such as Creutzfeldt-Jacob disease, from the administration of a pharmaceutical composition which contains human plasma protein concentrates, such as serum albumin.
Gelatin has been used in some protein active ingredient pharmaceutical compositions as an albumin substitute. Notably, gelatin is a animal derived protein and therefore carries the same risk of potential infectivity which may be possessed by human serum albumin. Hence, it is desirable to find a substitute for human serum albumin which is not a blood fraction, and preferably, the albumin substitute is not gelatin and is not derived from any animal (i.e. mammalian) source.
Botulinum Toxin
The anaerobic, gram positive bacterium Clostridium botulinum produces a potent polypeptide neurotoxin, botulinum toxin, which causes a neuroparalytic illness in humans and animals referred to as botulism. Clostridium botulinum and its spores are commonly found in soil and the bacterium can grow in improperly sterilized and sealed food containers of home based canneries, which are the cause of many of the cases of botulism. The effects of botulism typically appear 18 to 36 hours after eating the foodstuffs infected with a Clostridium botulinum culture or spores. The botulinum toxin can apparently pass unattenuated through the lining of the gut and attack peripheral motor neurons. Symptoms of botulinum toxin intoxication can progress from difficulty walking, swallowing, and speaking to paralysis of the respiratory muscles and death.
Botulinum toxin type A is the most lethal natural biological agent known to man. About 50 picograms of botulinum toxin (purified neurotoxin complex) type A is a LD50 in mice. Interestingly, on a molar basis, botulinum toxin type A is 1.8 billion times more lethal than diphtheria, 600 million times more lethal than sodium cyanide, 30 million times more lethal than cobrotoxin and 12 million times more lethal than cholera. Singh, Critical Aspects of Bacterial Protein Toxins, pages 63-84 (chapter 4) of Natural Toxins II, edited by B. R. Singh et al., Plenum Press, New York (1976) (where the stated LD50 of botulinum toxin type A of 0.3 ng equals 1 U is corrected for the fact that about 0.05 ng of BOTOX® equals 1 unit). One unit (U) of botulinum toxin is defined as the LD50 upon intraperitoneal injection into female Swiss Webster mice weighing 18-20 grams each. In other words, one unit of botulinum toxin is the amount of botulinum toxin that kills 50% of a group of female Swiss Webster mice.
Seven generally immunologically distinct botulinum neurotoxins have been characterized, these being respectively botulinum neurotoxin serotypes A, B, C1, D, E, F, and G, each of which is distinguished by neutralization with type-specific antibodies. The different serotypes of botulinum toxin vary in the animal species that they affect and in the severity and duration of the paralysis they evoke. For example, it has been determined that botulinum toxin type A is 500 times more potent, as measured by the rate of paralysis produced in the rat, than is botulinum toxin type B. Additionally, botulinum toxin type B has been determined to be non-toxic in primates at a dose of 480 U/kg which is about 12 times the primate LD50 for botulinum toxin type A. The botulinum toxins apparently bind with high affinity to cholinergic motor neurons, are translocated into the neuron and block the presynaptic release of acetylcholine.
Botulinum toxins have been used in clinical settings for the treatment of neuromuscular disorders characterized by hyperactive skeletal muscles. Botulinum toxin type A was approved by the U.S. Food and Drug Administration in 1989 for the treatment of essential blepharospasm, strabismus and hemifacial spasm in patients over the age of twelve. Clinical effects of peripheral injection (i.e. intramuscular or subcutaneous) botulinum toxin type A are usually seen within one week of injection, and often within a few hours after injection. The typical duration of symptomatic relief (i.e. flaccid muscle paralysis) from a single intramuscular injection of botulinum toxin type A can be about three months to about six months.
Although all the botulinum toxins serotypes apparently inhibit release of the neurotransmitter acetylcholine at the neuromuscular junction, they do so by affecting different neurosecretory proteins and/or cleaving these proteins at different sites. Botulinum toxin A is a zinc endopeptidase which can specifically hydrolyze a peptide linkage of the intracellular, vesicle associated protein SNAP-25. Botulinum type E also cleaves the 25 kiloDalton (kD) synaptosomal associated protein (SNAP-25), but targets different amino acid sequences within this protein, as compared to botulinum toxin type A. Botulinum toxin types B, D, F and G act on vesicle-associated protein (VAMP, also called synaptobrevin), with each serotype cleaving the protein at a different site. Finally, botulinum toxin type C1 has been shown to cleave both syntaxin and SNAP-25. These differences in mechanism of action may affect the relative potency and/or duration of action of the various botulinum toxin serotypes.
Regardless of serotype, the molecular mechanism of toxin intoxication appears to be similar and to involve at least three steps or stages. In the first step of the process, the toxin binds to the presynaptic membrane of the target neuron through a specific interaction between the heavy chain (H chain) and a cell surface receptor; the receptor is thought to be different for each serotype of botulinum toxin and for tetanus toxin. The carboxyl end segment of the H chain, HC, appears to be important for targeting of the toxin to the cell surface.
In the second step, the toxin crosses the plasma membrane of the poisoned cell. The toxin is first engulfed by the cell through receptor-mediated endocytosis, and an endosome containing the toxin is formed. The toxin then escapes the endosome into the cytoplasm of the cell. This last step is thought to be mediated by the amino end segment of the H chain, HN, which triggers a conformational change of the toxin in response to a pH of about 5.5 or lower. Endosomes are known to possess a proton pump which decreases intra endosomal pH. The conformational shift exposes hydrophobic residues in the toxin, which permits the toxin to embed itself in the endosomal membrane. The toxin then translocates through the endosomal membrane into the cytosol.
The last step of the mechanism of botulinum toxin activity appears to involve reduction of the disulfide bond joining the H and L chain. The entire toxic activity of botulinum and tetanus toxins is contained in the L chain of the holotoxin; the L chain is a zinc (Zn++) endopeptidase which selectively cleaves proteins essential for recognition and docking of neurotransmitter-containing vesicles with the cytoplasmic surface of the plasma membrane, and fusion of the vesicles with the plasma membrane. Tetanus neurotoxin, botulinum toxin B, D, F, and G cause degradation of synaptobrevin (also called vesicle-associated membrane protein (VAMP)), a synaptosomal membrane protein. Most of the VAMP present at the cytosolic surface of the synaptic vesicle is removed as a result of any one of these cleavage events. Each toxin specifically cleaves a different bond.
The molecular weight of the botulinum toxin protein molecule, for all seven of the known botulinum toxin serotypes, is about 150 kD. Interestingly, the botulinum toxins are released by Clostridial bacterium as complexes comprising the 150 kD botulinum toxin protein molecule along with associated non-toxin proteins. Thus, the botulinum toxin type A complex can be produced by Clostridial bacterium as 900 kD, 500 kD and 300 kD forms. Botulinum toxin types B and C1 are apparently produced as only a 500 kD complex. Botulinum toxin type D is produced as both 300 kD and 500 kD complexes. Finally, botulinum toxin types E and F are produced as only approximately 300 kD complexes. The complexes (i.e. molecular weight greater than about 150 kD) are believed to contain a non-toxin hemagglutinin protein and a non-toxin and non-toxic nonhemagglutinin protein. These two non-toxin proteins (which along with the botulinum toxin molecule can comprise the relevant neurotoxin complex) may act to provide stability against denaturation to the botulinum toxin molecule and protection against digestive acids when toxin is ingested. Additionally, it is possible that the larger (greater than about 150 kD molecular weight) botulinum toxin complexes may result in a slower rate of diffusion of the botulinum toxin away from a site of intramuscular injection of a botulinum toxin complex. The toxin complexes can be dissociated into toxin protein and hemagglutinin proteins by treating the complex with red blood cells at pH 7.3. The toxin protein has a marked instability upon removal of the hemagglutinin protein.
All the botulinum toxin serotypes are made by Clostridium botulinum bacteria as inactive single chain proteins which must be cleaved or nicked by proteases to become neuroactive. The bacterial strains that make botulinum toxin serotypes A and G possess endogenous proteases and serotypes A and G can therefore be recovered from bacterial cultures in predominantly their active form. In contrast, botulinum toxin serotypes C1, D, and E are synthesized by nonproteolytic strains and are therefore typically unactivated when recovered from culture. Serotypes B and F are produced by both proteolytic and nonproteolytic strains and therefore can be recovered in either the active or inactive form. However, even the proteolytic strains that produce, for example, the botulinum toxin type B serotype only cleave a portion of the toxin produced. The exact proportion of nicked to unnicked molecules depends on the length of incubation and the temperature of the culture. Therefore, a certain percentage of any preparation of, for example, the botulinum toxin type B toxin is likely to be inactive, possibly accounting for the known significantly lower potency of botulinum toxin type B as compared to botulinum toxin type A. The presence of inactive botulinum toxin molecules in a clinical preparation will contribute to the overall protein load of the preparation, which has been linked to increased antigenicity, without contributing to its clinical efficacy. Additionally, it is known that botulinum toxin type B has, upon intramuscular injection, a shorter duration of activity and is also less potent than botulinum toxin type A at the same dose level.
In vitro studies have indicated that botulinum toxin inhibits potassium cation induced release of both acetylcholine and norepinephrine from primary cell cultures of brainstem tissue. Additionally, it has been reported that botulinum toxin inhibits the evoked release of both glycine and glutamate in primary cultures of spinal cord neurons and that in brain synaptosome preparations botulinum toxin inhibits the release of each of the neurotransmitters acetylcholine, dopamine, norepinephrine, CGRP and glutamate.
High quality crystalline botulinum toxin type A can be produced from the Hall A strain of Clostridium botulinum with characteristics of ≧3×107 U/mg, an A260/A278 of less than 0.60 and a distinct pattern of banding on gel electrophoresis. The known Schantz process can be used to obtain crystalline botulinum toxin type A, as set forth in Schantz, E. J., et al, Properties and use of Botulinum toxin and Other Microbial Neurotoxins in Medicine, Microbiol Rev. 56: 80-99 (1992). Generally, the botulinum toxin type A complex can be isolated and purified from an anaerobic fermentation by cultivating Clostridium botulinum type A in a suitable medium. Raw toxin can be harvested by precipitation with sulfuric acid and concentrated by ultramicrofiltration. Purification can be carried out by dissolving the acid precipitate in calcium chloride. The toxin can then be precipitated with cold ethanol. The precipitate can be dissolved in sodium phosphate buffer and centrifuged. Upon drying there can then be obtained approximately 900 kD crystalline botulinum toxin type A complex with a specific potency of 3×107 LD50 U/mg or greater. This known process can also be used, upon separation out of the non-toxin proteins, to obtain pure botulinum toxins, such as for example: purified botulinum toxin type A with an approximately 150 kD molecular weight with a specific potency of 1-2×108 LD50 U/mg or greater; purified botulinum toxin type B with an approximately 156 kD molecular weight with a specific potency of 1-2×108 LD50 U/mg or greater, and; purified botulinum toxin type F with an approximately 155 kD molecular weight with a specific potency of 1-2×107 LD50 U/mg or greater.
Already prepared and purified botulinum toxins and toxin complexes suitable for preparing pharmaceutical formulations can be obtained from List Biological Laboratories, Inc., Campbell, Calif.; the Centre for Applied Microbiology and Research, Porton Down, U.K.; Wako (Osaka, Japan), as well as from Sigma Chemicals of St Louis, Mo.
It has been reported that BoNt/A has been used in clinical settings as follows:                (1) about 75-125 units of BOTOX®1 per intramuscular injection (multiple muscles) to treat cervical dystonia;        (2) 5-10 units of BOTOX® per intramuscular injection to treat glabellar lines (brow furrows) (5 units injected intramuscularly into the procerus muscle and 10 units injected intramuscularly into each corrugator supercilii muscle);        (3) about 30-80 units of BOTOX® to treat constipation by intrasphincter injection of the puborectalis muscle;        (4) about 1-5 units per muscle of intramuscularly injected BOTOX® to treat blepharospasm by injecting the lateral pre-tarsal orbicularis oculi muscle of the upper lid and the lateral pre-tarsal orbicularis oculi of the lower lid.        (5) to treat strabismus, extraocular muscles have been injected intramuscularly with between about 1-5 units of BOTOX®, the amount injected varying based upon both the size of the muscle to be injected and the extent of muscle paralysis desired (i.e. amount of diopter correction desired).        (6) to treat upper limb spasticity following stroke by intramuscular injections of BOTOX® into five different upper limb flexor muscles, as follows:        (a) flexor digitorum profundus: 7.5 U to 30 U        (b) flexor digitorum sublimus: 7.5 U to 30 U        (c) flexor carpi ulnaris: 10 U to 40 U        (d) flexor carpi radialis: 15 U to 60 U        (e) biceps brachii: 50 U to 200 U. Each of the five indicated muscles has been injected at the same treatment session, so that the patient receives from 90 U to 360 U of upper limb flexor muscle BOTOX® by intramuscular injection at each treatment session.        (7) to treat migraine, pericranial injected (injected symmetrically into glabellar, frontalis and temporalis muscles) injection of 25 U of BOTOX® has showed significant benefit as a prophylactic treatment of migraine compared to vehicle as measured by decreased measures of migraine frequency, maximal severity, associated vomiting and acute medication use over the three month period following the 25 U injection.        
Additionally, intramuscular botulinum toxin has been used in the treatment of tremor in patients with Parkinson's disease, although it has been reported that results have not been impressive. Marjama-Lyons, J., et al., Tremor-Predominant Parkinson's Disease, Drugs & Aging 16(4);273-278:2000.
It is known that botulinum toxin type A can have an efficacy for up to 12 months (European J. Neurology 6 (Supp 4): S111′-S1150:1999), and in some circumstances for as long as 27 months. The Laryngoscope 109:1344-1346:1999. However, the usual duration of an intramuscular injection of Botox® is typically about 3 to 4 months.
The success of botulinum toxin type A to treat a variety of clinical conditions has led to interest in other botulinum toxin serotypes. Additionally, pure botulinum toxin has been used in humans. see e.g. Kohl A., et al., Comparison of the effect of botulinum toxin A (Botox (R)) with the highly-purified neurotoxin (NT201) in the extensor digitorum brevis muscle test, Mov Disord 2000;15(Suppl 3):165 Hence, a pharmaceutical composition can be prepared using a pure botulinum toxin. The botulinum toxin molecule (about 150 kDa), as well as the botulinum toxin complexes (about 300-900 kDa), such as the toxin type A complex are also extremely susceptible to denaturation due to surface denaturation, heat, and alkaline conditions. Inactivated toxin forms toxoid proteins which may be immunogenic. The resulting antibodies can render a patient refractory to toxin injection.
As with enzymes generally, the biological activities of the botulinum toxins (which are intracellular peptidases) are dependant, at least in part, upon their three dimensional conformation. Thus, botulinum toxin type A is detoxified by heat, various chemicals surface stretching and surface drying. Additionally, it is known that dilution of the toxin complex obtained by the known culturing, fermentation and purification to the much, much lower toxin concentrations used for pharmaceutical composition formulation results in rapid detoxification of the toxin unless a suitable stabilizing agent is present. Dilution of the toxin from milligram quantities to a solution containing nanograms per milliliter presents significant difficulties because of the rapid loss of specific toxicity upon such great dilution. Since the toxin may be used months or years after the toxin containing pharmaceutical composition is formulated, the toxin must be stabilized with a stabilizing agent. To date, the only successful stabilizing agent for this purpose has been the animal derived proteins human serum albumin and gelatin. And as indicated, the presence of animal derived proteins in the final formulation presents potential problems in that certain stable viruses, prions, or other infectious or pathogenic compounds carried through from donors can contaminate the toxin.
Furthermore, any one of the harsh pH, temperature and concentration range conditions required to lyophilize (freeze-dry) or vacuum dry a botulinum toxin containing pharmaceutical composition into a toxin shipping and storage format (ready for use or reconstitution by a physician) can detoxify the toxin. Thus, animal derived or donor pool proteins such as gelatin and serum albumin have been used with some success to stabilize botulinum toxin.
A commercially available botulinum toxin containing pharmaceutical composition is sold under the trademark BOTOX® (available from Allergan, Inc., of Irvine, Calif.). BOTOX® consists of a purified botulinum toxin type A complex, human serum albumin, and sodium chloride packaged in sterile, vacuum-dried form.
The botulinum toxin type A is made from a culture of the Hall strain of Clostridium botulinum grown in a medium containing N-Z amine and yeast extract. The botulinum toxin type A complex is purified from the culture solution by a series of acid precipitations to a crystalline complex consisting of the active high molecular weight toxin protein and an associated hemagglutinin protein. The crystalline complex is re-dissolved in a solution containing saline and albumin and sterile filtered (0.2 microns) prior to vacuum-drying. BOTOX® can be reconstituted with sterile, non-preserved saline prior to intramuscular injection. Each vial of BOTOX® contains about 100 units (U) of Clostridium botulinum toxin type A complex, 0.5 milligrams of human serum albumin and 0.9 milligrams of sodium chloride in a sterile, vacuum-dried form without a preservative.
To reconstitute vacuum-dried BOTOX® sterile normal saline without a preservative (0.9% Sodium Chloride injection) is used by drawing up the proper amount of diluent in the appropriate size syringe. Since BOTOX® is denatured by bubbling or similar violent agitation, the diluent is gently injected into the vial. For sterility reasons, BOTOX® should be administered within four hours after reconstitution. During this time period, reconstituted BOTOX® is stored in a refrigerator (2° to 8° C.). Reconstituted BOTOX® is clear, colorless and free of particulate matter. The vacuum-dried product is stored in a freezer at or below −5° C.
Other commercially available botulinum toxin containing pharmaceutical compositions include Dysport® (Clostridium botulinum type A toxin hemagglutinin complex with human serum albumin and lactose in the formulation, available from Ipsen Limited, Berkshire, U.K. as a powder to be reconstituted with 0.9% sodium chloride before use), and MyoBloc™ (an injectable solution comprising botulinum toxin type B, human serum albumin, sodium succinate, and sodium chloride at about pH 5.6, available from Elan Corporation, Dublin, Ireland).
It has been reported that a suitable alternative to human serum albumin as a botulinum toxin stabilizer may be another protein or alternatively a low molecular weight (non-protein) compound. Carpender et al., Interactions of Stabilizing Additives with Proteins During Freeze-Thawing and Freeze-Drying, International Symposium on Biological Product Freeze-Drying and Formulation, 24-26 Oct. 1990; Karger (1992), 225-239.
Many substances commonly used as carriers and bulking agents in pharmaceutical compositions have proven to be unsuitable as albumin replacements in a Clostridial toxin containing pharmaceutical composition. For example, the disaccharide cellobiose has been found to be unsuitable as a botulinum toxin stabilizer. Thus, it is known that the use of cellobiose as an excipient in conjunction with albumin and sodium chloride results in a much lower level of toxicity (10% recovery) after lyophilization of crystalline botulinum toxin type A with these excipients, as compared to the toxicity after lyophilization with only human serum albumin (>75% to >90% recovery). Goodnough et al., Stabilization of Botulinum Toxin Type A During Lyophilization, App & Envir. Micro. 58 (10) 3426-3428 (1992).
Furthermore, saccharides, including polysaccharides, are in general poor candidates to serve as protein stabilizers. Thus, it is known that a pharmaceutical composition containing a protein active ingredient is inherently unstable if the protein formulation comprises a saccharide (such as glucose or a polymer of glucose) or carbohydrates because proteins and glucose are known to interact together and to undergo the well-described Maillard reaction, due to the reducing nature of glucose and glucose polymers. Much work has been dedicated to mostly unsuccessful attempts at preventing this protein-saccharide reaction by, for example, reduction of moisture or use of non-reducing sugars. Significantly, the degradative pathway of the Maillard reaction can result in a therapeutic insufficiency of the protein active ingredient. A pharmaceutical formulation comprising protein and a reducing saccharide, carbohydrate or sugar, such as a glucose polymer, is therefore inherently unstable and cannot be stored for a long period of time without significant loss of the active ingredient protein's desired biological activity.
Notably, one of the reasons human serum albumin can function effectively as a stabilizer of a protein active ingredient in a pharmaceutical composition is because, albumin, being a protein, does not undergo the Maillard reaction with the protein active ingredient in a pharmaceutical composition. Hence, one would expect to find and to look for a substitute for human serum albumin amongst other proteins.
Finding an appropriate substitute for human serum albumin as a stabilizer of the botulinum toxin present in a pharmaceutical composition is difficult and problematic because human serum albumin is believed to function in a pharmaceutical composition as more than a mere bulking agent. Thus, albumin apparently can interact with botulinum toxin so as to increase the potency of the neurotoxin. For example, it is known that bovine serum albumin can act as more than a mere stabilizing excipient for botulinum toxin type A, since bovine serum albumin apparently also accelerates the rate of catalysis of synthetic peptide substrates, which substrates resemble the SNAP-25 intraneuronal substrate for botulinum toxin type A Schmidt, et al., Endoproteinase Activity of Type A Botulinum Neurotoxin Substrate Requirements and Activation by Serum Albumin, J. of Protein Chemistry, 16 (1), 19-26 (1997). Thus, albumin may have a potentiating effect, apparently by affecting rate kinetics, upon the intracellular proteolytic action of a botulinum toxin upon the toxin's substrate. This potentiating effect may be due to albumin which has accompanied the botulinum toxin upon endocytosis of the toxin into a target neuron or the potentiating effect may be due to the pre-existing presence cytoplasmic albumin within the neuron protein prior to endocytosis of the botulinum toxin.
The discovery of the presence of a kinetic rate stimulatory effect by bovine serum albumin upon the proteolytic activity of botulinum toxin type A renders the search for a suitable substitute for albumin in a botulinum toxin containing pharmaceutical formulation especially problematic. Thus, an albumin substitute with desirable toxin stabilization characteristics may have an unknown and possibly deleterious effect upon the rate of substrate catalysis by the toxin, since at least with regard to bovine serum albumin the two characteristics (toxin stabilization and toxin substrate catalysis potentiation) are apparently inherent to the same albumin excipient. This potentiating effect of albumin shows that albumin does not act as a mere excipient in the formulation and therefore renders the search for a suitable substitute for albumin more difficult.
Additionally there are many unique characteristics of botulinum toxin and its formulation into a suitable pharmaceutical composition which constrain and hinder and render the search for a replacement for the albumin used in current botulinum toxin containing pharmaceutical formulations very problematic. Examples of four of these unique characteristics follow.
First, botulinum toxin is a relatively large protein for incorporation into a pharmaceutical formulation (the molecular weight of the botulinum toxin type A complex is 900 kD) and is therefore is inherently fragile and labile. The size of the toxin complex makes it much more friable and labile than smaller, less complex proteins, thereby compounding the formulation and handling difficulties if toxin stability is to be maintained. Hence, an albumin replacement must be able to interact with the toxin in a manner which does not denature, fragment or otherwise detoxify the toxin molecule or cause disassociation of the non-toxin proteins present in the toxin complex.
Second, as the most lethal known biological product, exceptional safety, precision, and accuracy is called for at all steps of the formulation of a botulinum toxin containing pharmaceutical composition. Thus, a preferred potential albumin replacer should not itself be toxic or difficult to handle so as to not exacerbate the already extremely stringent botulinum toxin containing pharmaceutical composition formulation requirements.
Third, since botulinum toxin was the first microbial toxin to be approved (by the FDA in 1989) for injection for the treatment of human disease, specific protocols had to be developed and approved for the culturing, bulk production, formulation into a pharmaceutical and use of botulinum toxin. Important considerations are toxin purity and dose for injection. The production by culturing and the purification must be carried out so that the toxin is not exposed to any substance that might contaminate the final product in even trace amounts and cause undue reactions in the patient. These restrictions require culturing in simplified medium without the use of animal meat products and purification by procedures not involving synthetic solvents or resins. Preparation of toxin using enzymes, various exchangers, such as those present in chromatography columns and synthetic solvents can introduce contaminants and are therefore excluded from preferred formulation steps. Furthermore, botulinum toxin type A is readily denatured at temperatures above 40 degrees C., loses toxicity when bubbles form at the air/liquid interface, and denatures in the presence of nitrogen or carbon dioxide.
Fourth, particular difficulties exist to stabilize botulinum toxin type A, because type A consists of a toxin molecule of about 150 kD in noncovalent association with nontoxin proteins weighing about 750 kD. The nontoxin proteins are believed to preserve or help stabilize the secondary and tertiary structures upon which toxicity is dependant. Procedures or protocols applicable to the stabilization of nonproteins or to relatively smaller proteins are not applicable to the problems inherent with stabilization of the botulinum toxin complexes, such as the 900 kD botulinum toxin type A complex. Thus while from pH 3.5 to 6.8 the type A toxin and non toxin proteins are bound together noncovalently, under slightly alkaline conditions (pH >7.1) the very labile toxin is released from the toxin complex. As set forth previously, pure botulinum toxin (i.e the 150 kD molecule) has been proposed as the active ingredient in a pharmaceutical composition.
In light of the unique nature of botulinum toxin and the requirements set forth above, the probability of finding a suitable albumin replacement for the human serum albumin used in current botulinum toxin containing pharmaceutical compositions must realistically be seen to approach zero. Prior to the present invention, only the animal derived proteins, human serum albumin and gelatin, had been known to have utility as suitable stabilizers of the botulinum toxin present in a pharmaceutical formulation. Thus, albumin, by itself or with one or more additional substances such as sodium phosphate or sodium citrate, is known to permit high recovery of toxicity of botulinum toxin type A after lyophilization. Unfortunately, as already set forth, human serum albumin, as a pooled blood product, can, at least potentially, carry infectious or disease causing elements when present in a pharmaceutical composition. Indeed, any animal product or protein such as human serum albumin or gelatin can also potentially contain pyrogens or other substances that can cause adverse reactions upon injection into a patient.
Chinese patent application CN 1215084A discusses an albumin free botulinum toxin type A formulated with gelatin, an animal derived protein. U.S. Pat. No. 6,087,327 also discloses a composition of botulinum toxin types A and B formulated with gelatin. These formulations therefore do not eliminate the risk of transmitting an animal protein derived or accompanying infectious element.
Acetylcholine
Typically only a single type of small molecule neurotransmitter is released by each type of neuron in the mammalian nervous system. The neurotransmitter acetylcholine is secreted by neurons in many areas of the brain, but specifically by the large pyramidal cells of the motor cortex, by several different neurons in the basal ganglia, by the motor neurons that innervate the skeletal muscles, by the preganglionic neurons of the autonomic nervous system (both sympathetic and parasympathetic), by the postganglionic neurons of the parasympathetic nervous system, and by some of the postganglionic neurons of the sympathetic nervous system. Essentially, only the postganglionic sympathetic nerve fibers to the sweat glands, the piloerector muscles and a few blood vessels are cholinergic as most of the postganglionic neurons of the sympathetic nervous system secret the neurotransmitter norepinephrine. In most instances acetylcholine has an excitatory effect. However, acetylcholine is known to have inhibitory effects at some of the peripheral parasympathetic nerve endings, such as inhibition of heart rate by the vagal nerve.
The efferent signals of the autonomic nervous system are transmitted to the body through either the sympathetic nervous system or the parasympathetic nervous system. The preganglionic neurons of the sympathetic nervous system extend from preganglionic sympathetic neuron cell bodies located in the intermediolateral horn of the spinal cord. The preganglionic sympathetic nerve fibers, extending from the cell body, synapse with postganglionic neurons located in either a paravertebral sympathetic ganglion or in a prevertebral ganglion. Since, the preganglionic neurons of both the sympathetic and parasympathetic nervous system are cholinergic, application of acetylcholine to the ganglia will excite both sympathetic and parasympathetic postganglionic neurons.
Acetylcholine activates two types of receptors, muscarinic and nicotinic receptors. The muscarinic receptors are found in all effector cells stimulated by the postganglionic, neurons of the parasympathetic nervous system as well as in those stimulated by the postganglionic cholinergic neurons of the sympathetic nervous system. The nicotinic receptors are found in the adrenal medulla, as well as within the autonomic ganglia, that is on the cell surface of the postganglionic neuron at the synapse between the preganglionic and postganglionic neurons of both the sympathetic and parasympathetic systems. Nicotinic receptors are also found in many nonautonomic nerve endings, for example in the membranes of skeletal muscle fibers at the neuromuscular junction.
Acetylcholine is released from cholinergic neurons when small, clear, intracellular vesicles fuse with the presynaptic neuronal cell membrane. A wide variety of non-neuronal secretory cells, such as, adrenal medulla (as well as the PC12 cell line) and pancreatic islet cells release catecholamines and parathyroid hormone, respectively, from large dense-core vesicles. The PC12 cell line is a clone of rat pheochromocytoma cells extensively used as a tissue culture model for studies of sympathoadrenal development. Botulinum toxin inhibits the release of both types of compounds from both types of cells in vitro, permeabilized (as by electroporation) or by direct injection of the toxin into the denervated cell. Botulinum toxin is also known to block release of the neurotransmitter glutamate from cortical synaptosomes cell cultures.
A neuromuscular junction is formed in skeletal muscle by the proximity of axons to muscle cells. A signal transmitted through the nervous system results in an action potential at the terminal axon, with activation of ion channels and resulting release of the neurotransmitter acetylcholine from intraneuronal synaptic vesicles, for example at the motor endplate of the neuromuscular junction. The acetylcholine crosses the extracellular space to bind with acetylcholine receptor proteins on the surface of the muscle end plate. Once sufficient binding has occurred, an action potential of the muscle cell causes specific membrane ion channel changes, resulting in muscle cell contraction. The acetylcholine is then released from the muscle cells and metabolized by cholinesterases in the extracellular space. The metabolites are recycled back into the terminal axon for reprocessing into further acetylcholine.
Hydroxyethyl Starch
A polysaccharide can be made up of hundreds or even thousands of monosaccharide units held together by glycoside (ether) linkages. Two important polysaccharides are cellulose and starch. Cellulose is the chief structural material in plants, giving plants their rigidity and form. Starch makes up the reserve food supply of plants and is found mainly in various seeds and tubers.
Starch occurs as granules whose size and shape are characteristic of the plant from which the starch is obtained. In general about 80% of starch is a water insoluble fraction called amylopectin. Amylopectin is made up of chains of D-glucose (as glucopyranose) units, each unit being joined by an alpha glycoside linkage to C-4 of the next glucose unit. Like starch, cellulose is also made up of chains of D-glucose units, where each unit is joined by a glucoside linkage to the C-4 of the next unit. Unlike starch though, the glycoside linkages in cellulose are beta linkages. Treatment of cellulose with sulfuric acid and acetic anhydride yields the disaccharide cellobiose. As previously set forth, attempts to stabilize botulinum toxin using cellobiose have been unsuccessful.
A particular starch derivative which can be obtained by treating starch with pyridine and ethylene chlorohydrin, is 2-hydroxyethyl starch, also called hetastarch. U.S. Pat. No. 4,457,916 discloses a combination of a nonionic surfactant and hydroxyethyl starch to stabilize aqueous solutions of tumor necrosis factor (TNF).
Additionally, a 6% aqueous solution of 2-hydroxyethyl starch (hetastarch) (available from Du Pont Pharma, Wilmington, Del. under the trade name HESPAN®, 6% hetastarch in 0.9% sodium chloride injection) is known. Albumin is known to act as a plasma volume expander upon intravenous administration to a patient. HESPAN® has also been administrated to patients to achieve a plasma volume expansion effect and in that sense intravenous HESPAN® can be considered a replacement for intravenous albumin.
Hetastarch is an artificial colloid derived from a waxy starch composed almost entirely of amylopectin. Hetastarch can be obtained by introducing hydroxyethyl ether groups onto glucose units of the starch, and the resultant material can then be hydrolyzed to yield a product with a molecular weight suitable for use as a plasma volume expander. Hetastarch is characterized by its molar substitution and also by its molecular weight. The molar substitution can be approximately 0.75, meaning that hetastarch is etherified to the extent that for every 100 glucose units of hetastarch there are, on average, approximately 75 hydroxyethyl substituent groups. The average molecular weight of hetastarch is approximately 670 kD with a range of 450 kD to 800 kD and with at least 80% of the polymer units falling within the range of 20 kD to 2,500 kD. Hydroxyethyl groups are attached by ether linkages primarily at C-2 of the glucose unit and to a lesser extent at C-3 and C-6. The polymer resembles glycogen, and the polymerized D-glucose units are joined primarily by α-1,4 linkages with occasional α-1,6 branching linkages. The degree of branching is approximately 1:20, meaning that there is an average of approximately one α-1,6 branch for every 20 glucose monomer units. Hetastarch is comprised of more than 90% amylopectin.
The plasma volume expansion produced by HESPAN® can approximate that obtained with albumin. Hetastarch molecules below 50 kD molecular weight are rapidly eliminated by renal excretion and a single dose of approximately 500 mL of HESPAN® (approximately 30 g) results in elimination in the urine of approximately 33% of the administered HESPAN® within about 24 hours. The hydroxyethyl group of hydroxyethyl starch is not cleaved in vivo, but remains intact and attached to glucose units when excreted. Significant quantities of glucose are not produced as hydroxyethylation prevents complete metabolism of the smaller hydroxyethyl starch polymers
Cellulose can likewise be converted to a hydroxyethyl cellulose. The average molecular weight of 2-hydroxyethyl cellulose (a 2-hydroxyethyl ether of cellulose) is about 90 kD. Unfortunately, hydroxyethyl cellulose, unlike hydroxyethyl starch, is highly reactive and therefore unsuited for use as a stabilizer of a protein active ingredient in a pharmaceutical formulation.
Pharmaceutical Compositions for Veterinary Use
Non human animals (or “animals” in this section) can suffer from maladies and injuries that are painful and difficult to treat. For example, some canine breeds, such as German Shepherds, commonly suffer from hip dysplasia, and may require corrective surgery, such as hip replacement. Horses may suffer from gastrointestinal disorders, such as colic, that may result in significant pain. Similarly, race horses frequently suffer from fractured or broken bones. Horses may also suffer flexor tendon and suspensory ligament injury. Ponies are particularly susceptible to founder, a painful crippling disorder specific to horses. Additionally, juvenile birds, such as parrots can be afflicted with scoliosis
Additionally, non human animals may be subjected to painful and irreversible procedures, such as denervation, to modify involuntary natural behaviors, for example ear and tail twitching, in show horses for example. Such drastic procedures are performed for cosmetic reasons. No other humane remedy currently exists to correct such undesirable traits. These procedures permanently damage the animals.
Animals may also cause severe injury to themselves due to what would be a mild condition in humans. Wounds are often exacerbated by stall rubbing in horses resulting in insufficient healing and chronic sores. Sores and skin irritation can result in serious infection in this manner. Other maladies not seen in human patients exist in animals. For example, flies and parasites cause discomfort and act as vectors for disease. Dogs often require hospitalization and or restraint due to biting and scratching related to fleas and mange. Collars are often placed around the animal's neck to prevent the animal from scratching ears affected by mites or surgical procedures. These maladies, if mediated for a time sufficient for the affected area to heal or the parasite to be removed, can be avoided, relieving the animal of suffering and symptoms.
A significant barrier in treating animals and promoting their recovery from injury or surgery is due to an inability to instruct the animal about proper rest and rehabilitation procedures. The difficulty of immobilizing an animal may result in re-injury, self-injury, and/or improper healing. Minor injuries often become catastrophic due to the difficulty of immobilizing animals during and after treatment. Many times the animal must be destroyed. In addition, wild animals (e.g., non-domestic animals) that pose a danger to others or themselves may need to be immobilized to safely return the animal to its native environment. Typically, these animals are tranquilized and moved, or are killed.
Another problem when treating animals arises from the difficulty in administering proper dosages. Animals do not readily swallow oral dosage forms of medicine and often offer violent resistance to injections. Frequent application of short-acting drugs may therefore not be possible. Accordingly, as opposed to humans, animals may require long-acting, single injection pharmaceuticals to receive adequate benefit from the drug.
While pharmaceutical compositions containing human protein may not present problems from a single administration, except in certain individuals or species, repeated dosing may initiate immune responses in animals, including anaphylactic shock. As discussed above, current formulations of botulinum toxin include human serum albumin (HSA) as a stabilizing excipient. These formulations may present serious problems for veterinary use because the presence of a human protein may induce immunogenic responses in other animal species, limiting the efficacy, utility, and safety of the drug. Formulations which do not contain HSA as an excipient, however, should not produce these antibodies. The lack of suitable formulations of botulinum toxin for use in treating non-human animals has impeded the development of methods of using botulinum toxin in veterinary medicine.
Indeed, the majority, if not all, of research regarding the therapeutic aspects of botulinum toxin has focused on the use of botulinum toxin for treating human diseases or ailments. As a necessary precursor, botulinum toxin has experimentally been administered to animals to examine its safety and efficacy in animal models of human diseases. For example, botulinum toxin type B has been administered to mice to treat thermal hyperalgesia (Tsuda et al., (1999) “In vivo pathway of thermal hyperalgesia by intrathecal administration of β-methylene ATP in mouse spinal cord: Involvement of the glutamate-NMDA receptor system”, Br. J. Pharmacol., 127(2):449-456). In addition, botulinum toxin type A has been:                administered to piglets to relieve lower esophageal sphincter (LES) pressure (U.S. Pat. No. 5,437,291, entitled “Method for treating gastrointestinal muscle disorders and other smooth muscle dysfunction”);        injected into gastric wall of rats to treat obesity (Gui et al., (2000) “Botulinum toxin injected in the gastric wall reduces body weight and food intake in rats”, Aliment Pharmacol Ther., 14(6):829-834);        used to assess the efficacy of the neurotoxin to produce better scar formation from facial cosmetic surgery in non-human primates (Gassner et al., (2000) Plast. Reconst. Surg., 105(6):1948-1953);        administered to rats to examine its ability to reduce pain (Aoki et al., (2000) “Methods for treating pain”, U.S. Pat. No. 6,113,915;        administered to rats and dogs to alter vocal cord dynamics for treating spasmodic dysphonia and vocal cord paralysis in humans (Inagi et al., (1998) “Physiologic assessment of botulinum toxin effects in the rat larynx”, Laryngoscope, 108(7):1048-1054; and Cohen and Thompson (1987) “Use of botulinum toxin to lateralize true vocal cords: a biochemical method to relieve bilateral abductor vocal cord paralysis”, Ann. Otol. Rhinol. Laryngol., 96(5):534-41); and        administered to the obicularis ocuji muscle of the guinea pig to examine the efficacy of the toxin to treat eye lid spasms (Horn et al., (1993) “Botulinum toxin paralysis of the orbicularis oculi muscle. Types and time course of alterations in muscle structure, physiology and lid kinematics”, Exp. Brain Res., 96(1):39-53).        
In addition, a botulinum toxin has been administered to rabbits to assess the immunogenicity of the toxin when conjugated with human serum albumin (HSA).
Because the administration of botulinum toxin to animals has only been examined experimentally as a model for treating humans with botulinum toxin, researchers have not been concerned with long-term effects of the neurotoxin on animals. In particular, the art has not addressed the immunogenicity of the botulinum toxin compositions in the non-human animals receiving the neurotoxin. Thus, it would be beneficial to have a neurotoxin composition with reduced immunogenicity for use in veterinary care, and convenient and effective methods for immobilizing or treating non-human animals.
What is needed therefore is a botulinum toxin containing pharmaceutical composition which is free of animal derived proteins such as a blood pooled or blood fraction derived serum albumin or gelatin.